The invention relates to a process for dewaxing a wax-containing hydrocarbon oil.
Dewaxing is an important process which is applied in the refining of hydrocarbon oils, since the removal of the wax leads to an oil with a considerably improved pour point. The process is usually carried out by cooling the oil to a temperature that is low enough to cause the wax to precipitate and then removing the wax from the oil by filtration. Usually, solvents are added to the oil which can dissolve the oil and precipitate the wax. The precipitated wax has a tendency to block the filter during the filtration. As a consequence, the filtration rate is substantially reduced and the quantity of oil remaining behind in the filter cake increases considerably. These difficulties can be avoided by carrying out the dewaxing in the presence of certain polymers, which are referred to as dewaxing aids. An example of a class of polymers suitable for this purpose is formed by polymers from one or more olefinically unsaturated compounds which consist at least partly of alkylacrylates or alkylmethacrylates with at least 8 carbon atoms in the alkyl group (referred to hereinafter as C.sub.8+ alkyl esters).
In an investigation by the applicant into the use of polymers as dewaxing aids, a class of polymers was found, which polymers were found to be extremely well suited for this purpose. On comparing the behavior of these polymers with that of the C.sub.8+ alkyl ester polymers, it can be seen that in a number of cases the previously mentioned polymers have a higher activity. This means that in comparison with the C.sub.8+ alkyl ester polymers, in a number of cases the polymers investigated by the applicant for this purpose give, at an equal concentration, a greater increase in the filtration rate and/or a greater reduction in the quantity of oil remaining behind in the filter cake, or that a given increase in the filtration rate and/or reduction in the quantity of oil remaining behind in the filter cake can be obtained at a lower concentration. The polymers having improved dewaxing capabilities are linear polymers of carbon monoxide with one or more olefins which consist at least partly of .alpha.-olefins with at least 10 carbon atoms per molecule (hereinafter referred to as C.sub.10+ .alpha.-olefins), wherein in these polymers monomer units of carbon monoxide and olefins are present in a substantially alternating arrangement.
In the investigation by the applicant into the use of polymers as dewaxing aids, it was further found that mixtures of polymers selected from each of the two above-mentioned classes are also very suitable for use as dewaxing aids.